John Mayer was also in attendance) for Katy's third studio album 'Prism,' which drops Oct. 22, and later posted the photo above to Instagram along with the tweet:

Maybe Katy can return the love when Rihanna's second fashion collection for River Island launches next month. The 80-piece collection is described as a mix of "urban sports lux with sophisticated chic," and includes items like skirts, jumpers and a range of underwear.

"I literally designed everything I want to wear, exactly how I want to wear it," Rihanna said. "We're giving it a New York street vibe."

The Autumn/Winter 2013 collection launches a "first wave" on Sept. 12, with a "second wave" due in November.